Semiconductor grade silicon is conventionally grown as a single crystal from a molten batch of polysilicon contained in a fused quartz vessel. The Czochralski method for doing so draws a single crystal silicon rod from the molten polysilicon mass at elevated temperatures often exceeding 1450.degree. C. and which now is carried out in a batch or continuous manner. Careful control of the operating temperatures must be exercised for numerous reasons to maintain a satisfactory yield of the semiconductor material being produced in such manner. To illustrate, in a typical manufacturing method heaters are employed along with heat shields to carefully control both axial and radial temperatures in the melt. By controlling temperature along with the rod pulling rate in said method, the diameter of the growing crystal is thereby controlled. As a single crystal is being pulled in such batch type process operation, the melt level in the crucible container also drops so that automatically controlled elevation of said crucible is commonly employed to avert undesired changes in the thermal profile during the growth process. It can thereby be appreciated that controlling the temperature distribution in this method remains a critical consideration.
Similarly, careful temperature control is exercised when producing a silicon semiconductor element by doping the above described single crystal material at elevated temperatures with a gaseous atmosphere containing a doping element. In this commercial process, the single crystal material is heated in a closed vessel of fused quartz and the gaseous atmosphere admitted for thermal diffusion of the doping element into the single crystal material. The fused quartz vessel commonly employed is a hollow cylinder closed at both ends which is often fabricated with optically clear fused quartz so as to enable penetration of the infrared heating energy being again supplied from surrounding heater elements. Since undesirable temperature fluctuations can occur in said diffusion process from heat losses experienced in a variety of ways, the control of temperature distribution in this equipment also remains important. It becomes desirable, therefore, to modify the fused quartz material now used in the overall thermal processing of semiconductor grade silicon in a manner which helps control the temperature distribution during the particular processing operations.